1. Field of the Invention
The present invention relates to an advanced liquid cooling apparatus, and more specifically to a liquid cooling apparatus which circulates a liquid refrigerant around electronic equipment, such as a TV transmitter, which generates heat.
2. Description of the Related Art
In general, an electronic apparatus such as a TV transmitter comprises multiple printed circuit boards on which many semiconductor devices are provided, in its own rack. A fan or a blower attached inside or outside the rack performs forced-air cooling for the printed circuit board.
In recent years, since many circuitry elements are integrated as large scale or mounted in high-density packaging, the density of the heating locations in the rack increases. Such apparatus frequently makes use of a liquid cooling method which provides a high heat exchange performance. For example, to transfer heat outside, a liquid refrigerant is provided and flows on a flat board (cold plate), on which circuitry elements are disposed.
As shown in FIG. 7, in a conventional cooling system, the liquid refrigerant circulates around an electronic apparatus 50, which generates heat, removing the heat from the electronic apparatus 50. In FIG. 7, reference numeral 50 denotes an electronic apparatus which generates heat; reference numeral 60 denotes a pump rack; and reference numeral 70 denotes a heat exchange unit to cool the liquid.
Reference numerals 51 and 52 denote cold plates in the electronic apparatus. Reference numerals 53 and 54 denote copper pipes in the cold plates 51 and 52. Reference numeral 55 denotes a pipe arrangement which is connected to a return pipe arrangement 83. Reference numeral 61 in a pump rack 60 denotes a tank which absorbs possible volume changes caused by the temperature change of the liquid refrigerant. Reference numeral 62 denotes a pump to send the liquid refrigerant to the electronic apparatus 50. Reference numeral 63 denotes a pipe which is used to connect a transmission pipe arrangement 81 to the pump 62. The reference numeral 64 is a pipe arrangement which is used to connect the tank 61 to the pump 62. Reference numeral 65 denotes a pipe arrangement which is used to connect the tank 61 to the return pipe arrangement 82.
Reference numeral 71 in the heat exchange unit 70 denotes a condenser which is used for heat exchange. Reference numeral 72 denotes a fan. Reference numeral 73 denotes a motor to rotate the fan 72. Reference numeral 74 denotes a pipe arrangement which is used to connect the return pipe arrangement 82 to the condenser 71. Reference numeral 75 denotes a pipe arrangement which is used to connect the condenser 71 to the return pipe arrangement 83.
FIG. 8 shows a detailed configuration of the cold plate 51 as shown in FIG. 7. In FIG. 8, reference numeral 2 denotes a semiconductor device such as a power transistor (a heating unit, hereinafter). Reference numeral 3 denotes a lead wire of the heating unit. Reference numeral 53 denotes a copper pipe in the cold plate 51. Reference numeral 56 denotes grease used for the radiation of heat, where the heat of the cold plate 51 is transmitted to the copper pipe 53.
In the above conventional cooling system using the cold plate, however, since the cold plate, the grease and the copper pipe lie therebetween, it becomes difficult to efficiently transfer the heat of the heating unit to the liquid refrigerant. Thereby, there is a problem that cooling operation cannot be done efficiently.
In addition, in the case where several heating units are placed in a dispersed manner, a large and heavy cold plate is necessary to cover the whole of the heating units. This requires an apparatus large in size.
Furthermore, when grease is coated between the copper pipe and the cold plate for efficient heat transfer, the grease becomes reduced due to age deterioration and, thus, air-layers are naturally generated. These air-layers increase the thermal resistance. Thereby, there is a problem that stability and reliability of the apparatus become low.
On the other hand, it is noted that grease for efficient heat transfer may be unnecessary when aluminum material which embodies the cold plate is cast around the copper pipe. This can solve the problem of the low stability and reliability of the above mentioned prior art. However, cast-made aluminum material is inferior by 25% in thermal conductivity in comparison to ordinary aluminum material. Therefore, this leads to another problem that the cooling efficiency further deteriorates.